In an elevator system similar to that described in U.S. Pat. No. 5,202,540, entitled "Two-Way Ring Communication System for Elevator Group Control" (filed Mar. 23, 1987), the disclosure of which is incorporated herein by reference, elevator group control may be distributed among separate microprocessors, one per car in the group. These microprocessors, known as operational control subsystems (OCSS), are all connected together in a two-way ring network. Each OCSS has a number of other subsystems and signaling devices, etc., associated with it, as will be described more fully below; only one such collection of subsystems and signaling devices is illustrated in FIG. 1 for the sake of simplicity.
The hall buttons and lights are connected with remote stations and remote serial communication links to the OCSS via a switch-over module. The car buttons, light, and switches are connected through similar remote stations and serial links to the OCSS. The car specific hall features, such as car direction and position indicators, are connected through remote stations and remote serial link to the OCSS.
The car load measurement is periodically read by the door control subsystem (DCSS), which is part of the car controller. This load is sent to the motion control subsystem (MCSS), which is also part of the car controller. This load in turn is sent to the OCSS. DCSS and MCSS are microprocessors controlling door operation and car motion under the control of the OCSS, with the MCSS working in conjunction with the drive and brake subsystem (DBSS).
The dispatching function is executed by the OCSS, under the control of an advanced dispatcher subsystem (ADSS), which communicates with the OCSS via an information control subsystem (ICSS). The car load measured may be converted into boarding and deboarding passenger counts using the average weight of a passenger by the MCSS and sent to the OCSS. The OCSS sends this data to the ADSS via ICSS.
The ADSS through signal processing inter alia collects the passenger boarding and deboarding counts at the various floors and car arrival and departure counts, so that in accordance with its programming, it can analyze the traffic conditions at each floor. The ADSS can also collect other data for use in making predictions, etc., if so desired.
This ring system has problems.
Communication between each node in the system is point-to-point, i.e. from, for example, the drive control to the motion control or from the motion control to the operational control. Nodes are any communications element on a bus. If it is desired to move a message from the drive control to the operational control, the message must take two transmissions-one transmission from the drive control to the motion control and a second transmission from the motion control to the operational control. Because communication is point-to-point, the time required for communication is increased; the message must pass through many communication nodes, be decoded, interpreted, and encoded at each node along the message route. For the same reason, the communications computing requires complicated, expensive, and redundant software.
Second, this communication system requires that an applications microprocessor associated with a node perform communications functions in addition to the application functions for which the host microprocessor was designed, for example, in the case of the drive and brake subsystem, directing movement of the machine and sheave and brake. Therefore, the microprocessors, such as the DBSS, do not perform their applications as well as they might.
Third, it is difficult to add a node to the system; doing so requires each node in the communications path between the transmitting node and the receiving node to be loaded with the hardware and software for transmitting and receiving messages from the transmitting node, even though this intermediary node is not going to use that message. For example, if EMS wants to send a message to ADSS, then ICSS 1 and each OCSS within the communications path, as well as ICSS 2, must be retrofitted with the hardware and software for handling an EMS message. This need for retrofitting each intermediary node with the hardware and software for a message is more pernicious when not only is this particular message not meant for the intermediary transceiver node (for example OCSS), but none of the messages from the transmitting node (for example, EMS) are ever used by the intermediary node for performing its main function.